This invention pertains to a film magnetic transducer head and more particularly to an improved film transducer head having an improved combination of writing and reading capabilities.
In a magnetic transducer, a given combination of pole tip and gap dimensions, film thickness and yoke geometry using high saturation magnetization alloy have proved to be superior to a high permeability alloy with respect to the ability to write high coercivity recording media. A typical high saturation magnetization alloy is 45/55 nickel-iron (Ni Fe) and a common high permeability alloy is 81/19 Ni Fe. At the location where the pole tip region initially saturates, the high saturation magnetization 45/55 Ni Fe alloy permits more flux to be transmitted to the pole tips and to the recording media. Typical thin film transducer head strutures having a yoke structure formed of a single magnetic material is shown in U.S. Pat. No. 4,190,872.
Unfortunately, heads made of 45/55 Ni Fe alloy also exhibited two problems: there is a relatively large irreproducibility in signal amplitude, and the readback amplitude is low. The standard deviation of amplitudes after successive write operations is typically 10 percent for 45/55 Ni Fe heads whereas in a typical product using 81/19 Ni Fe heads, there is an amplitude deviation specification of less than 4 percent. The reason for this scatter is not fully understood, although it is known to be associated with high positive magnetostriction materials and irreproducible domain structures in the head. These irreproducible and unsymmetrical domains are particularly prevalent in the back portions of the head. Closure domains in the pole tip region, although in principle undesirable, are more regular and reproducible in occurrence. The readback amplitude of 45/55 Ni Fe heads is relatively low because of the lower permeability of the material, typically 1300-1400 as compared to 2000-2500 81/19 Ni Fe. For a given geometry, lower permeabilities give rise to lower head efficiencies.